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# Dumb Math Question

## Are you smarter than a 5th grader?

#### Dabu The Dragon

1:38 am on Nov 20, 2007 (gmt 0)

#### Junior Member

joined:Dec 13, 2003
posts:109

Well, I'm not. Maybe you are.

Trying to help my kid with his math work. Trying not to look too dumb here. Can one of you WebmasterWorld math wizards help us out?

Problem:

One number is 6 more than another. If the sum of the smaller number and 3 times the larger number is 34, find the two numbers.

#### blend27

1:56 am on Nov 20, 2007 (gmt 0)

#### Senior Member

joined:Dec 27, 2004
posts:1665

4 and 10?

#### phranque

1:58 am on Nov 20, 2007 (gmt 0)

joined:Aug 10, 2004
posts:10542

One number is 6 more than another. If the sum of the smaller number and 3 times the larger number is 34, find the two numbers.

two equations, two unknowns:
x=y+6
y+3x=34

substitute for x in the second equation and solve for y.
substitute for y in the first equation and solve for x.

#### phranque

1:59 am on Nov 20, 2007 (gmt 0)

joined:Aug 10, 2004
posts:10542

4 and 10?

you get an F for not showing your work!

#### blend27

2:03 am on Nov 20, 2007 (gmt 0)

#### Senior Member

joined:Dec 27, 2004
posts:1665

-F-

phranque, i am Russian, i do it in my head :),

#### jdMorgan

2:05 am on Nov 20, 2007 (gmt 0)

#### Senior Member

joined:Mar 31, 2002
posts:25430

I'm sure there is a shorter, more formal way to do this, but here you go. "S" is the small number, "L" is the larger.

Two equations given:
1) L=S+6
2) S+3xL=34

Using equation #1, substitute (S+6) for L in Equation #2:
S+3x(S+6)=34

Convert 3x(S+6) to 3xS + 3x6:
S+3xS+3x6=34

3x6=18:
4xS+18=34

Subtract 18 from both sides of the equation:
4xS=16

Divide both sides of the equation by 4:
S=4

If S=4, and L=S+6, then L must be 10:

Plug the numbers back into equation #2 to test it:
4+(3x10)=34

Jim

#### rj87uk

2:06 am on Nov 20, 2007 (gmt 0)

#### Senior Member

joined:Mar 30, 2004
posts:1148

two equations, two unknowns:
x=y+6
y+3x=34

substitute for x in the second equation and solve for y.
substitute for y in the first equation and solve for x.

Let me guess, PHP, SQL & Basic pro or just good at maths?!

#### blend27

2:17 am on Nov 20, 2007 (gmt 0)

#### Senior Member

joined:Dec 27, 2004
posts:1665

Speaking of Math:

this link is to the video, i hope its ok

#### phranque

2:19 am on Nov 20, 2007 (gmt 0)

joined:Aug 10, 2004
posts:10542

phranque, i am Russian, i do it in my head :),

when a 5th grader asks for help in math, the worst thing you can do is give him/her the answer (only).

Let me guess, PHP, SQL & Basic pro or just good at maths?!

no php, plenty of sql, no basic of any flavor for decades, plenty of math way back when, kids in school...

#### blend27

2:24 am on Nov 20, 2007 (gmt 0)

#### Senior Member

joined:Dec 27, 2004
posts:1665

#### phranque

2:29 am on Nov 20, 2007 (gmt 0)

joined:Aug 10, 2004
posts:10542

the F was a joke...

#### inbound

3:03 am on Nov 20, 2007 (gmt 0)

#### Senior Member

joined:Oct 9, 2004
posts:1435

Surely this is much simpler as you know that one number is 6 less than the higher number you can look for 4 times the higher number knowing without worrying about the lower number until you have the first answer (no need to overcomplicate the logic on this one):

3x + (x - 6) = 34

>> Which simplifies to

4x - 6 = 34

>> move the 6 over (changing the sign)

4x = 34 + 6

4x = 40

>> Dividing gives

x = 10

>> Find smaller number

y = x - 6

>> which gives

y = 4

>> Hence (after checking 3*10 + 1*4 = 34)

Larger number = 10
Smaller number = 4

#### Dabu The Dragon

3:15 am on Nov 20, 2007 (gmt 0)

#### Junior Member

joined:Dec 13, 2003
posts:109

Now I can look smarter than I really am. WebmasterWorld to the rescue once again. Thanks.

#### vincevincevince

3:22 am on Nov 20, 2007 (gmt 0)

#### Senior Member from MY

joined:Apr 1, 2003
posts:4847

I agree that it's not good to give a 5th grader the answer to an algebra problem, in addition I don't think you should give them the method. Teaching methods is what the school has done, the homework is evidently designed to stretch the 5th grader's ability to reformulate the problem intuitively. More time (as long as it takes), a mug of coffee, and a room with no distractions are the best way for a student to solve a mathematics problem.

#### blend27

3:57 am on Nov 20, 2007 (gmt 0)

#### Senior Member

joined:Dec 27, 2004
posts:1665

initialy I thought it backwords though:

34=3(x+6)+x; came up with the lower number first;

#### jdancing

4:51 am on Nov 20, 2007 (gmt 0)

#### Senior Member

joined:Feb 18, 2003
posts:745

Yahoo answers is my son's friend when I can't help him ;)

#### Habtom

5:25 am on Nov 20, 2007 (gmt 0)

#### Senior Member

joined:Nov 15, 2004
posts:1867

you get an F for not showing your work!

Maybe at school, but surely not in real life :)

#### phranque

6:06 am on Nov 20, 2007 (gmt 0)

joined:Aug 10, 2004
posts:10542

Trying to help my kid with his math work.

sounds like school to me...

#### Dabrowski

3:57 pm on Nov 21, 2007 (gmt 0)

#### Senior Member

joined:Mar 29, 2007
posts:1147

In the UK we have a TV program called 'Are You Smarter than a 10 Year Old'. While I'm not sure how old a 5th grader is, older than that by the looks of the question, I'm regularly astounded at some people's lack of knowledge of anything.

Some bloke works for 10 hours, and sleeps for 8. In it's simplest form, what fraction of the day does he work?

Another:
What is the young of a Kangaroo called?

I can't believe people don't know this stuff!

#### phranque

4:15 pm on Nov 21, 2007 (gmt 0)

joined:Aug 10, 2004
posts:10542

While I'm not sure how old a 5th grader is, older than that by the looks of the question,...

a typical 5th grader would be 10-11 years old.
and now that you mention it algebra isn't usually taught in 5th grade - that must be some school.

#### Dabrowski

4:27 pm on Nov 21, 2007 (gmt 0)

#### Senior Member

joined:Mar 29, 2007
posts:1147

mention it algebra isn't usually taught in 5th grade

Particularly with double unknowns.

#### LifeinAsia

5:01 pm on Nov 21, 2007 (gmt 0)

#### Moderator from US

joined:Dec 10, 2005
posts:5550

Some bloke works for 10 hours, and sleeps for 8. In it's simplest form, what fraction of the day does he work?

Another:
What is the young of a Kangaroo called?

Not being able to perform (fairly) basic math is one problem, not being able to recall (or never having learned) a bit of trivia that isn't critical in real life (unless you're on Jeopardy and that's the question for Final Jeopardy) is another story.

On the other hand, if you lived in Australia and couldn't answer the 2nd question...

[edited by: LifeinAsia at 5:02 pm (utc) on Nov. 21, 2007]

#### timster

5:31 pm on Nov 21, 2007 (gmt 0)

#### Senior Member

joined:Aug 1, 2003
posts:815

algebra isn't usually taught in 5th grade - that must be some school

We got a recommendation spit out by a computer from school that we work on Geometry with our 5th grader. Okeedoke.

And yes, some of the homework my 5th grade has been bringing home looks a lot like Algebra. I think it's supposed to be "guess and check" but some of the kids are using variable substitution because it's quicker.

#### lgn1

5:02 pm on Nov 23, 2007 (gmt 0)

#### Senior Member

joined:Nov 12, 2003
posts:1070

Its easy, and your kid will never have a problem solving a series of non-homogenous linear equations again.

#### vincevincevince

1:48 am on Nov 24, 2007 (gmt 0)

#### Senior Member from MY

joined:Apr 1, 2003
posts:4847

Dabu The Dragon, I assume you're not a programmer? In my opinion, the best way to learn algebra for a kid is to learn to write programmes. Nowhere else will constantly be challenged to write and solve equations of all levels of complexity whilst thoroughly enjoying themselves.

Pick a comprehensive but syntactically simple language such as a BASIC derivative and teach the kid how to build simple apps, games, toys etc. As a childhood hobby it is very engaging and involving and has the side effects of high intellectual stimulation at very minimal ongoing investment compared to most hobbies.